Method of reshaping and ion-exchanging glass

ABSTRACT

A molded glass article is produced by pressing a body of molten glass which is sufficiently hot to be electrically conductive between two complementary mold parts to produce an article of a required shape, and passing an electric current through the glass between solid electrically conductive electrodes in direct contact with the molded faces of the glass to impart a desired surface characteristic to at least one of the molded faces of the glass.

1 1 1 1 limited Mates Watemrt 1 15] 3mm M Lonlres 1 Well. 11., 11972[54] METHUIU UH WESHAPHNG AND llUN- 2,707,688 5/1955 Blackman ..65/30 XEXQHANGHNG GLASfi 3,218,220 11/1965 Weber 3,450,581 6/1969 Shortes....[72] lnventor: David G. lboulres, Presco't, England 3,502,022 3/ 1970Wood Assisnee: Wilmington Emma Liverpool 3,244,497 4/1966 Copeland..65/356 X England Primary Examiner-Arthur D. Kellogg 2 Filed: 7 9 9Attorney-Morrison, Kennedy & Campbell! [21] Appl. No.: 822,592

[30] Foreign Application Priority Data [57] ABSTRACT Ma 14, 1968 GreatBritain ..22,901/68 A molded glass article is produced by pressing abody of molten glass which is sufficiently hot to be electricallyconductive 521 1U.S.1C1 "as/3o, 65/77, 65/104, between two complementarymold Parts to produce an article 65/268 65/275 of a required shape, andpassing an electric current through l the glass between solidelectrically conductive electrodes in 5 182 direct contact with themolded faces of the glass to impart a desired surface characteristic toat least one of the molded faces of the glass.

[56] li telierencescited v V 4 {1C1aims,3DrawinglFigures UNITED STATESPATENTS 1,592,429 7/1926 Kraus ..65/60 X S 00/6 19 F /4l 5 i\ K O 5 '"7i f5 j PATENTEDFEB m1? 3,639,114

Inventor DAVID GQRDON LOUKES 2) I l WWW! AtrneyS METHOD 01F RESIHIAIPINGAND IION-EXCHANGING GLASS BACKGROUND OF THE INVENTION This inventionrelates to the production of moulded glass articles. The invention isparticularly, but not exclusively, applicable to the manufacture ofglass articles having predetermined surface characteristics other thanthose inherent in the method of forming the articles.

SUMMARY According to the present invention in one aspect thereof amethod of producing a moulded glass article comprises pressing a body ofmolten glass which is sufficiently hot to be electrically conductivebetween two complementary mould parts to produce an article of arequired shape, and passing an electric current through the glassbetween solid electrically conductive electrodes in direct contact withthe moulded faces of the glass to impart a desired surfacecharacteristic to at least one of the moulded faces of the glass.

The solid electrodes may be metallic or may be formed of carbon.Conveniently, the mould parts are electrically con ductive andthemselves constitute the two electrodes.

Alternating current may be passed through the glass to effeet heating ortreatment of the moulded article. Where a direct current is passedbetween the electrodes, surface treatment of the moulded glass may beeffected by forming the positive electrode of, or including in thepositive electrode, an element which is capable of producing a requiredsurface characteristic when incorporated in the glass, said elementforming positive ions which enter the glass surface upon passage of thecurrent.

The positive electrode may comprise or contain cobalt, copper, gold,iron, nickel or silver.

The invention also provides apparatus for producing a moulded glassarticle, said apparatus comprising two relatively movable mould partshaving complementary mould surfaces, means for introducing molten glassto be moulded between the mould parts, solid electrically conductiveelectrodes adapted to make direct contact with the moulded faces of theglass, and an electrical current source connected to said electrodes forpassing a current through the moulded glass between the electrodes toimpart a desired surface characteristic to at least one of the mouldedfaces of the glass.

The mould parts may be electrically conductive and themselves constitutethe two electrodes.

One or both of the mould parts may be provided with internal channelsfor the circulation of a coolant fluid, for example, water.

The invention further comprehends a'moulded glass article having desiredsurface characteristics produced by the method as hereinbeforedescribed.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more clearlyunderstood from the following description, given by way of example, withreference to the accompanying drawings in which:

FIG. I is a diagrammatic cross section by way of example, through aglass moulding apparatus according to the invention.

FIG. 2 is a sectional elevationthrough the glass half-brick treated inExample I, and

FIG. 3 illustrates a circuit for obtaining the direct current componentof the electrolytic process used in Example ll.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I illustrates a mould forforming hollow glass articles in the form of half-bricks.

A gob of glass to be moulded is delivered from a furnace (not shown) inconventional manner at a temperature of the order of 950 C., at whichtemperature the glass is at a suitable viscosity of moulding and is alsoelectrically conductive.

The hot glass is moulded between two mould parts having complementarymould surfaces conforming to the required shape of the glass article tobe moulded. The two mould parts are operated at conventional mouldtemperatures for the particular material from which the mould parts areformed, that is in the case of the mould parts being formed of carbon orcobalt, up to temperatures of the order of 600 C. The mould parts may beprotected by a nonoxidizing atmosphere.

In the illustrated embodiment the mould comprises a horizontallydisposed outer mould part 2 formed of cobalt and an inner mould part 3,shown as a plunger of iron or carbon, which is mounted on a conventionalpress (not shown) for movement vertically relative to the outer mouldpart 2. The gob of molten glass is delivered into the lower mould part2, when the plunger 3 is retracted, and then the press is operated toforce the plunger into the molten glass in the mould so that when themould parts 2 and 3 are in their closed position, as shown, the moltenglass is pressed to the desired shape, as indicated at 4.

The outer and inner mould parts 2 and 3 are connected to he positive andnegative terminals respectively of a direct current electrical powersource 5, so that the outer mould part 2 is an anode and the inner mouldpart 34 a cathode of an electrolytic circuit, the glass 4 being theelectrolyte. Positive ions, in this case cobalt ions, pass from thesurface of the outer mould part 2 which is contacted by the glass intothe exterior face of the glass article as it is being formed and imparta surface characteristic (in this case, a blue tint) to the outer faceof the glass.

It is expedient to use the mould parts 2 and 3 as the anode and cathoderespectively for the electrolytic treatment of the glass as it is beingmoulded into a finished article, an alternative method is to perform theelectrolytic treatment after moulding but while the moulded glassarticle is still hot, by placing separate electrically conductiveelectrodes which are shaped to match intimately the dimensions of themoulded article in direct contact with the moulded glass surfaces.

The outer mould part 2 is provided with internal passages 6 for thecirculation of a coolant fluid, conveniently water. In the course oftime the outer mould part 2, or the positive elec trode, is consumed andrequires replacement. To facilitate this the mould part 2 is preferablyin the form of a replaceable lining to a metallic mould shell 7.

The inner mould part 3, or negative electrode, acquires during theelectrolytic process a coating of sodium metal due to the neutralizationof sodium ions which migrate from the glass. From time to time, orbetween successive moulding operations, this sodium coating is removedby heating the mould part 3 to vaporize the sodium.

Examples of other metals which may be used as, or included in, the outerpart 2 (or positive electrode) to produce surface modification of theglass by incorporation therein are: copper, gold, iron, nickel andsilver.

Use of any one of these metals imparts a different color to the treatedsurface. Also, in the case of a glass article having a surface treatedwith copper by the above described electrolytic process, subsequentheating of the article in an oxidizing atmosphere, for example at 600 C.converts the blue electrolytic copper ions into a blue/green mixture ofcuprous and cupric ions. On the other hand, subsequent heating of theelectrolytically treated article in a reducing atmosphere, again at 600C., converts the electrolytic copper ions into red colloidal particlesof copper.

If the article is treated electrolytically to cause migration of gold,nickel, silver or cobalt ions into the glass, subsequent heating in areducing atmosphere, e.g., percent nitrogen, 10 percent hydrogen,converts these metal ions in the glass into colloidal form, givingrespectively a red, grey/brown, yellow or grey color to the glass.

Although the process specifically illustrated related to the surfacetreatment of the external surface of the moulded glass article, theinterior surface of the article can equally well be treated by providingan inner mould part Fl of suitable material for modifying the interiorsurface and making the inner mould part 3 the anode and the outer mouldpart 2 the cathode of the electrolytic circuit.

Also, the inner mould part 3 may be provided with internal passages 6for the circulation of a coolant fluid.

As an alternative to passing direct current through the glass, analternating current could be passed therethrough for effecting surfacetreatment of both the interior and exterior faces of the moulded glassarticle concurrently.

A heating alternating current may be passed through the glass, e.g., byinjecting the alternating current into the direct current supply.

Any article of pressed ware may be produced with a desired surfacefinish by the method of the invention, for example a moulded glassinsulator can be produced with a metallic finish giving a desiredsurface resistivity to the insulator.

Two specific examples of the electrolytic process described above willnow be described.

Examplel This example concerned the electrolytic treatment of theoutside surface of the glass half-brick shown in FIG. 2. This half-brickis 19 cm. square and 5 cm. thick. The base of the half-brick has aminimum thickness of 6 mm. and the inside surface of the base has ribs11. The outside surface of the base 10 is formed with a 3 mm. deeprecess 12. The total outside area of the half-brick to be contacted bythe anode is about 741 sq. cm.

In order to impart a cobalt blue color with 65 percent lighttransmission, to the outside surface of the half-brick, it has beenfound that a current density of l coulombs/3 sq. cm. is required. Inthis case, therefore, about 247 coulombs were required.

The electrolytic process was switched on for 30 seconds with the appliedvoltage automatically adjusted to apply 7.5 amps. The actual voltage wasinitially 2 volts but rose during the operation of the process 10 voltsdue to polarization effects building up in the glass surface beingtreated and due to cooling of the glass.

The glass temperature at the beginning of the process was 950 C. and atthe end of the process it had dropped to 800 C.

The plunger 3 and the mould 2 were both provided with internal channels7 for the circulation of cooling air. However, the cooling air was onlyswitched on after the completion of the electrolytic process. The glasstemperature then fell to about 600 C. after about 3 minutes. The plunger3 was then withdrawn and the treated glass half-brick was removed fromthe mould 3.

The half-brick was transferred to a welding station and immediatelywelded to a second glass half-brick which had been similarly treated.The total effective light transmission of the colored brick was then 65percent X 65 percent which equals 42 percent.

Example II This example concerns an equivalent glass half-brick to thatemployed in Example I. However, in this case, the half-brick was heatedby alternating current superimposed on the direct electrolytic current.The temperature of the glass was thus maintained at 950 C., therebyallowing the electrolytic process to be carried out more quickly withoutsevere polarization effects building up, even though the plunger 3 andthe mould were, in this example, internally water cooled.

At the completion of the electrolytic process, the glass temperaturefell to 500 C. in about 1 minute, this being due to the more efficientwater cooling. Also, in this case, the water cooling was employedthroughout the electrolytic process. The mould and plunger surfaces werethus cooler and it was also found that there was a greatly reducedtendency for the glass to adhere to the mould or to the plunger. Indeed,the glass half-brick was readily removed from the mould at 500 C.

In this example, the alternating current was 590 amps at 18 volts andthe direct current was 49 amps at 45 volts. The electrolysis time was 5seconds.

A typical electrical supply circuit as illustrated in FIG. 3. In

this circuit, a supply is fed to a variable autotransformer 13 which isconnected to the primary winding of a second transformer 14 which iscapable of delivering high currents at relatively low voltages. One endof the secondary winding of the transformer 14 is connected to the mould2 by a line 15, and the other end of the secondary winding is connectedby a line 16 to the plunger 3. Two variable resistors R,, R, areconnected in parallel with each other and in series with the plunger. Adiode rectifier 18 is connected in series with the resistor R and anammeter 17 is connected in series with both the resistors R R and theplunger 3. A voltmeter 19 is connected across the lines '15, 16. Ifdesired, either or both the ammeter 17 and the voltmeter 19 could beconnected between the transformer 14 and the resistors R R instead ofbetween the resistors and the plunger 3, as shown.

Adjustment of resistor R controls the electrolytic direct currentcomponent flowing through the glass, and adjustment of the resistor R,controls the heating alternating current component.

We claim:

1. Apparatus for producing a moulded glass article, said apparatuscomprising two relatively movable, electrically conductive, mould partsconstituting electrodes and having complementary the mould parts, meansfor causing relative movement between said mould parts to deform saidglass so as to shape the article to a predetermined form, and anelectrical current source connected to said electrodes for passing acurrent through the moulded glass between the electrodes to impart adesired surface characteristic to the moulded face of the glass incontact with said one of the mould surfaces by ionexchange material intosaid moulded glass face.

2. A method of producing a moulded glass article and imparting a desiredsurface characteristic to at least one moulded surface thereof, themethod comprising:

applying solid electrically conductive surfaces, at least one of whichis formed with ion-exchange material, to heat softened glass disposedbetween said surfaces with a force sufi'icient to deform the glass so asto shape the article to a predetermined form; and

passing an electric current between said ion-exchange material surfaceand the heat softened glass, while the glass remains in a heat softenedstate and while said solid electrically conductive surfaces remain incontact with the deformed glass, so as to 'effect an ion-exchangematerial into a surface of said deformed glass in contact therewith.

3. A method according to claim 2, in which said ionexchange material isa metal selected from the following group: cobalt, copper, gold, iron,nickel and silver.

4. A method of producing a moulded glass article and imparting a desiredsurface characteristic to at least one moulded surface thereof, themethod comprising:

applying solid electrically conductive surfaces, at least one of whichis formed with ion-exchange material, to heat softened glass disposedbetween said surfaces with a force sufficient to deform the glass so asto shape the article to a predetermined form; and

simultaneously passing a direct electric current in a direction fromsaid ion-exchange material surface into the heat softened glass so as toeffect an ion-exchange from said ion-exchange material into a mouldedsurface of the glass article in contact therewith.

rNirrn STATES PATIENT orricn CERTll lCAlE or EQRREQTWN Patent No.3,639,114 Dated February 1, 1972 Inventofls) David G. Loukes It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

IN THE CLAIMS Column 4, line 29 before "the mould parts" insert --mouldsurfaces, at least one of said mould surfaces being formed withion-exchange material, means for introducing molten glass to be mouldedbetween".

Column 4, line 36 after "exchange" insert -from said ion-exchange",

Column 4, line 50 before "material" insert from said ion-exchange.

Signed and sealed this 19th day of February 197M.

(SEAL) Attest:

EDWARD M.FLETCHER,JRQ MARSHALL A Attesting Offi Commissioner of PatentsFORM PO-1050 (10-69) USCOMM-DC 5O376-P59 US. GOVERNMENT PRINTING OFFICE:I968 0-365-334

2. A method of producing a moulded glass article and imparting a desiredsurface characteristic to at least one moulded surface thereof, themethod comprising: applying solid electrically conductive surfaces, atleast one of which is formed with ion-exchange material, to heatsoftened glass disposed between said surfaces with a force sufficient todeform the glass so as to shape the article to a predetermined form; andpassing an electric current between said ion-exchange material surfaceand the heat softened glass, while the glass remains in a heat softenedstate and while said solid electrically conductive surfaces remain incontact with the deformed glass, so as to effect an ion-exchangematerial into a surface of said deformed glass in contact therewith. 3.A method according to claim 2, in which said ion-exchange material is ametal selected from the following group: cobalt, copper, gold, iron,nickel and silver.
 4. A Method of producing a moulded glass article andimparting a desired surface characteristic to at least one mouldedsurface thereof, the method comprising: applying solid electricallyconductive surfaces, at least one of which is formed with ion-exchangematerial, to heat softened glass disposed between said surfaces with aforce sufficient to deform the glass so as to shape the article to apredetermined form; and simultaneously passing a direct electric currentin a direction from said ion-exchange material surface into the heatsoftened glass so as to effect an ion-exchange from said ion-exchangematerial into a moulded surface of the glass article in contacttherewith.